To date, the nuclear accidents at the Chernobyl (1986) and Fukushima Daiichi (2011) nuclear power plants are the only INES level 7 nuclear accidents.
Chernobyl and Fukushima nuclear accidents The following table compares the Chernobyl and Fukushima nuclear accidents.
Plant Name Chernobyl Fukushima Daiichi Location Soviet Union (Ukrainian Soviet Socialist Republic) Japan Date of the accident April 26, 1986 March 11, 2011 INES Level 7 Plant commissioning date 1977 1971 Years of operation before the accident 9 years (plant) 40 years (plant) Electrical output plant (net): 3700 MWe (4 reactors)reactors (net): 925 MWe (Units 1–4) plant (net): 4546 MWe (6 reactors)reactors (net): 439 MWe (Unit 1), 760 MWe (Units 2–5), 1067 MWe (Unit 6) Type of reactor RBMK-1000 graphite moderated, 2nd generation reactor without containment BWR-3 and BWR-4 reactors with Mark I containment vessels Number of reactors 4 on site; 1 involved in accident 6 on site; 4 (and spent fuel pools) involved in accident; one of the four reactors was empty of fuel at the time of the accident. Amount of nuclear fuel in affected reactors 1 reactor—190 tonnes (t, metric tons = 210 U.S. short tons): spent fuel pools not involved in incident - note that figures were converted into US tons 4 reactors—854 tonnes (t, metric tons): 81 t in Unit 1 reactor, 111 t in Unit 2 reactor, 111 t in Unit 3 reactor, 0 t in Unit 4 reactor (defueled), 59 t in Unit 1 spent fuel pool (SFP), 119 t in Unit 2 SFP, 104 t in Unit 3 SFP, and 269 t in Unit 4 SFP Cause of the accident Proximate cause was human error and violation of procedures. The unsafe reactor design caused instability at low power due to a positive void coefficient and steam formation. When an improper test was conducted at 1:23 AM at low power, the reactor became prompt critical. This was followed by a steam explosion that exposed the fuel, a raging fire, and a core meltdown. The fire lasted for days to weeks, and there is controversy over whether it was the fuel burning, nuclear decay heating or whether the graphite moderator that made up most of the core was involved. See Chernobyl Disaster, Note 1, for more discussion. The plants were not designed with consideration of such a large tsunami concurrently occurring with the ground sinking. Subsequent review did not lead to mitigation. A major earthquake and tsunami caused the destruction of power lines and backup generators. Once the plants were without external power and the generators were flooded, a catastrophic decay heat casualty ensued, leading to major reactor plant damage including meltdowns. Maximum level of radiation detected 300 Sv/h shortly after the explosion in vicinity of the reactor core. 530 Sv/h inside Unit 2 containment vessel in 2017 according to Japan Times. Radioactivity released According to IAEA, total release was . in iodine-131 equivalent As of 2014, a peer reviewed estimate of the total was 340–780 PBq, with 80% falling into the Pacific Ocean. Radiation continues to be released into the Pacific via groundwater. Area affected An area up to away contaminated, according to the United Nations. Radiation levels exceeding annual limits seen over to northwest and to south-southwest, according to officials. Exclusion Zone Area 30 km 20 km (30 km voluntary) extending north-west to 45 km in the downwind direction to Iitate, Fukushima Population relocated 335,000 (About 115,000 from areas surrounding the reactor in 1986; about 220,000 people from Belarus, the Russian Federation and Ukraine after 1986) 154,000 Population returned None 122,000 Direct fatalities from the accident Two immediate trauma deaths; 28 deaths from acute radiation syndrome out of 134 showing symptoms; four from an industrial accident (helicopter crash); 15 deaths from radiation-genic thyroid cancers (as of 2005); as many as 4,000 to 90,000 cancer related deaths. 1 confirmed cancer death attributed to radiation exposure by the government for the purpose of compensation following opinions from a panel of radiologists and other experts, medical sources pending for long-term fatalities due to the radiation. Current status All reactors were shut down by 2000. The damaged reactor was covered by a hastily built steel and concrete structure called the sarcophagus. A New Safe Confinement structure was installed in November 2016, from which the plant will be cleaned up and decommissioned. Cold shutdown declared on 16 December 2011, but decommissioning is likely to take 30 to 40 years. All fuel rods in reactor 4 pool removed. Fukushima disaster cleanup is ongoing.
Radioactive contamination discharge
Report date Place Period Iodine-131(TBq) Caesium-137(TBq) Source from to from to 2002 Chernobyl 25 April – June 1986 1,600,000 1,940,000 59,000 111,000NEA2002, archived from Original on 20 April 2011, retrieved on 6 April 2011.22 March 2011 Fukushima 12 – 15 March 2011 400,000 3,000 30,000ZAMG. ZAMG, 22 March 2011, archived from Original on 20 April 2011, retrieved on 20 April 2011.2 April 2011 12 – 19 March 2011 10,000 700,001 1,000 70,000ZAMG. In: www.zamg.ac.at. Zentralanstalt für Meteorologie und Geodynamik, 2 April 2011, archived from Original on 20 April 2011, retrieved on 2 April 2011.12 April 2011 11 March – 5 April. JAIF / NHK, 26 April 2011, archived from Original on 27 April 2011, retrieved on 27 April 2011. 150,000 12,000NSC. NISA/METI, 12 April 2011, archived from Original on 12 April 2011, retrieved on 12 April 2011.12 April 2011 11 – 17 March 2011 130,000 6,100NISA 7 June 2011 160,000 15,000NISA. NISA/Kantei, 7 June 2011, archived from Original, retrieved on 8 June 2011.24 Aug. 201111 March – 5 April 130,000 11,000NSC. In: Atoms in Japan. JAIF, 5 September 2011, archived from Original, retrieved on 20 December 2011.15 Sept. 2011March – September100,000200,00010,00020,000Kantei. Kantei, 15 September 2011, archived from Original, retrieved on 17 December 2011. Spent fuel pool measurement on page 205, 207, 210 and 214; total release on page 449.
Report date Place Period Amount(TBq) Source 12 April 2011 Chernobyl 25 April – June 1986 5,200,000NISA Fukushima 11 March – 5 April 2011 630,000NSC 11 – 17 March 2011 370,000NISA April 2011 4 April 2011 154 NSC 25 April 2011 24 April 2011 24 6–7 June 2011 11 – 17 March 2011 770,000NISA. NHK, 6 June 2011, archived from Original, retrieved on 6 June 2011.7 June 2011 840,000NISA,. NISA/Kantei, 7 June 2011, archived from Original, retrieved on 14 June 2011. press printing17 August 2011 3–16 August 2011 0.07 Government. JAIF / NHK, 18 August 2011, archived from Original, retrieved on 21 August 2011. Converted from 200 MBq/h in a two-week period.23 August 2011 12 March - 5 April 2011 630,000NISAEarthquake Report – JAIF, No. 182. JAIF / NHK, 23 August 2011.
Report date Period Into the sea(TBq) Sourcedirectindirect21 May 20111 – 6 April 2011 4,700Tepco. Tepco, 21 May 2011, archived from Original, retrieved on 23 May 2011.End of August 2011March – August 2011 3,500 16,000JMADagmar Röhrlich: . In: dradio.de, Forschung Aktuell. Deutschlandfunk, 5 September 2011, archived from Original, retrieved on 7 September 2011; 1 000 000 000 000 Becquerel = 1 TBq.8 September 2011March – April 2011 15,000Scientist Group. JAIF / NHK, 9 September 2011, archived from Original, retrieved on 11 December 2011.29 October 201121 March – 15 July 2011 27,100IRSN. JAIF / NHK, 30 November 2011, archived from Original, retrieved on 20 December 2011.
See also Comparison of Chernobyl and other radioactivity releases Deaths due to the Chernobyl disaster List of accidents at the Mayak facility
Notes
References
External links How Much Fuel Is at Risk at Fukushima? Chernobyl Accident. World Nuclear Association. Fukushima Nuclear Crisis Unwrapped Fukushima Nuclear Accident. IAEA Update Log BBC News: Fukushima and Chernobyl compared